Bookmark and Share

Notice: On March 31, it was announced that Statalist is moving from an email list to a forum. The old list will shut down on April 23, and its replacement, statalist.org is already up and running.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: R: st: problem of data management


From   Nick Cox <njcoxstata@gmail.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: R: st: problem of data management
Date   Wed, 17 Apr 2013 18:54:32 +0100

-todate- (SSC) is a user-written command, as you are asked to explain.

-todate- is for run-together dates. It served a purpose from the time
it was written to Stata 10, when the official function -date()- became
smarter about date strings without separators. Now it serves no
purpose, unless you are using Stata 9 or earlier and have run-together
dates.

You have separators in your dates, not run-together dates, so -date()-
in official Stata should work fine.

It's a puzzle why you told -todate- that mm/dd/yyyy dates were
yyyymmdd,   as that doesn't match. Any way, -todate- from your
instructions expects strings of length at most 8, and your pattern
doesn't match that because of the embedded slashes.

gen date3 = date(date, "MDY")

should work for you. See -help dates and times- first for your next
date problem.
Nick
njcoxstata@gmail.com


On 17 April 2013 18:43, Iodice Federico <federico.iodice@hotmail.it> wrote:
> dear statalister i've a new problem,
>
>
> With respect to the previous email, we have a string as a data in the following format:
>
> 12/06/2007, which means mm/dd/yyyy i have tried to following todate command (after downloading it):
>
> todate date, generate(date3) pattern(yyyymmdd)
>
> I get the following error message:
>
> date: length does not match pattern
>
> how to solve the problem? We need to transform the string to a date format.
>
> ----------------------------------------
>> Date: Mon, 15 Apr 2013 23:52:26 +0100
>> Subject: Re: R: st: problem of data management
>> From: njcoxstata@gmail.com
>> To: statalist@hsphsun2.harvard.edu
>>
>> Thanks for the further detail. It is now evident that you do not have
>> duplicates (in the sense of -duplicates-) that can or should be
>> removed. You may be able to -xtset- your data using your identifier
>> variable and a date variable or you may just -xtset- your data using
>> the identifier variable.
>> Nick
>> njcoxstata@gmail.com
>>
>>
>> On 15 April 2013 21:56, Iodice Federico <federico.iodice@hotmail.it> wrote:
>> > we have included, for shortness sake only few variables, which makes some observations look like duplicate. However, the observation that looks like a duplicate is not a duplicate. It refers in fact to the same individual being observed again, but with a different outcome variable. To show this, we have added a different column to show what we mean:
>> >
>> > ID GENDER AGE TIME Outcome Sector
>> > 861 woman 50-54 1 861 Petrol & gas
>> > 848 woman 25-29 1 848 consumer goods
>> > 820 man 50-54 1 820 consumer goods
>> > 861 woman 50-54 1 869 Petrol & gas
>> > 820 man 50-54 1 870 services
>> > 860 woman 50-54 1 890 services
>> > 860 woman 50-54 2 895 consumer goods
>> > 860 woman 50-54 1 900 consumer goods
>> >
>> > In other words, the same individual has been observed another time, because she has found a new job. I hope it is now clear what we mean. In fact, there are also other variables that are different, such as the time when the new contract has been signed, the type of contract and so on.
>> >> Date: Mon, 15 Apr 2013 10:04:24 +0100
>> >> Subject: Re: R: st: problem of data management
>> >> From: njcoxstata@gmail.com
>> >> To: statalist@hsphsun2.harvard.edu
>> >>
>> >> Same answer from me. From what you tell us, a wide structure would not
>> >> make most conceivable analyses easier.
>> >>
>> >> Your example included
>> >>
>> >> ID GENDER AGE TIME
>> >> 861 woman 50-54 1
>> >> 861 woman 50-54 1
>> >>
>> >> so that on that information duplicates could be inferred.
>> >>
>> >> I don't think your example included enough detail for us to advise
>> >> well on how to create a time (meaning date) variable. Presumably that
>> >> depends on other variables that you don't show us. Much depends on
>> >> whether you want the date variable to make sense across identifiers.
>> >>
>> >> Nick
>> >> njcoxstata@gmail.com
>> >>
>> >>
>> >> On 15 April 2013 09:33, Iodice Federico <federico.iodice@hotmail.it> wrote:
>> >> > Sorry, probably I was not clear in the description of my data management
>> >> > problem,
>> >> >
>> >> > the TIME column in the example below is not a time variable, it identifies
>> >> > instead the type of working contract an individual has got: 1 is assigned to
>> >> > Part-time contracts and 2 is assigned to full-time contracts.
>> >> >
>> >> > The ID column doesn't have duplicates, but different observations of the
>> >> > same ID in different moments.
>> >> >
>> >> > In the ID variable, individuals have several occurrences, but the time when
>> >> > the individual is observed again and again has no regularity, are not
>> >> > defined a priori. We are observing individuals whenever they find a new job.
>> >> > Sometimes, they have many short employment spells. Quite often they find a
>> >> > permanent job and then we do not observe them anymore.
>> >> >
>> >> > For that reasons, I thought that it could have been a better solution to
>> >> > transform the dataset in wide format. This would mean dealing with it not as
>> >> > a panel data set, but rather as a cross-section with a longitudinal
>> >> > dimension.
>> >> >
>> >> > The alternative hypothesis would be to maintain the long format that the
>> >> > data set naturally has but since the ID variable is repeated only for some
>> >> > cases, for this reason I need to create a time variable to assign a sequence
>> >> > to successive observations of the same individual. This would be important
>> >> > to implement the xtset command. In other words, to maintain the long format
>> >> > and use panel data analysis, I need a command that assigns a
>> >> > growing numerical value to the new time variable. It should be done
>> >> > automatically every time the same individual is observed again. We have
>> >> > several thousands of observations.
>> >>
>> >> >> > Date: Tue, 9 Apr 2013 11:59:24 +0100
>> >> >> > From: njcoxstata@gmail.com
>> >> >> >
>> >> >> > You can -xtset- your data using
>> >> >> >
>> >> >> > xtset id
>> >> >> >
>> >> >> > but your example indicates that you have duplicates on -id time-, so
>> >> >> >
>> >> >> > xtset id time
>> >> >> >
>> >> >> > would fail. I don't think you are telling us enough for it to be clear
>> >> >> > whether you just have -duplicates- (see the command of that name) that
>> >> >> > should be remove.ì
>> >> >> >
>> >> >> > I can't see any advantages to your wide data structure (Example 2).
>> >> >> > (Many people do call this a format.)
>> >> >> >
>> >> >> > Nick
>> >> >> > njcoxstata@gmail.com
>> >> >> >
>> >> >> >
>> >> >> > On 9 April 2013 11:51, Iodice Federico <federico.iodice@hotmail.it> wrote:
>> >> >> >
>> >> >> >> I have a problem of data management that I would like to submit to your
>> >> >> attention. I’ve an unbalanced panel databank. As you can see from the
>> >> >> example below, the variable in column 1 (the ID variable) is repeated only
>> >> >> for some cases. In other words, I have the same individual who is repeated
>> >> >> several times.
>> >> >> >>
>> >> >> >> Example 1
>> >> >> >>
>> >> >> >> ID GENDER AGE TIME
>> >> >> >> 861 woman 50-54 1
>> >> >> >> 848 woman 25-29 1
>> >> >> >> 820 man 50-54 1
>> >> >> >> 861 woman 50-54 1
>> >> >> >> 820 man 50-54 1
>> >> >> >> 860 woman 50-54 1
>> >> >> >> 860 woman 50-54 2
>> >> >> >> 860 woman 50-54 1
>> >> >> >>
>> >> >> >> This happens only for some, but not all individuals in the sample. It
>> >> >> means that probably the best way of dealing with this dataset is to use it
>> >> >> not as a panel, but as a longitudinal data set with repeated observations.
>> >> >> The observations that do not repeat themselves, I can treat as staying in
>> >> >> the same status.
>> >> >> >> In order to use this information, my impression is that I need either:
>> >> >> >>
>> >> >> >> a) to tell to Stata that this is a panel and treat the data as if it
>> >> >> >> were a “long format”; If case a) is the best one, the data is in the long
>> >> >> format and I need only to tell to Stata that the same observation is
>> >> >> repeated for different periods. Nonetheless, these periods are not fixed.
>> >> >> There can be any length, from one week to several years. how to tell to
>> >> >> stata that the same observation is repeated several times? How to define the
>> >> >> time dimension?
>> >> >> >>
>> >> >> >> b) or to treat the data as a cross-section with repeated observations. In
>> >> >> this case, I need to move the rows that are repeated to the to shift
>> >> >> automatically the entire repeated line to the right of the first line in
>> >> >> which the variable y appears. An example of case b) is below. My question
>> >> >> is: how to move the entire row besides the one where that observation is
>> >> >> already defined?
>> >> >> >>
>> >> >> >> Example 2
>> >> >> >>
>> >> >> >> ID GENDER AGE TIME ID GENDER AGE TIME ID GENDER AGE TIME
>> >> >> >> 861 woman 50-54 1 861 woman 50-54 1
>> >> >> >> 848 woman 25-29 1
>> >> >> >> 820 man 50-54 1 820 man 50-54 1
>> >> >> >> 860 woman 50-54 1 860 woman 50-54 2 860 woman 50-54 1
>> >>
>> >> *
>> >> * For searches and help try:
>> >> * http://www.stata.com/help.cgi?search
>> >> * http://www.stata.com/support/faqs/resources/statalist-faq/
>> >> * http://www.ats.ucla.edu/stat/stata/
>> > *
>> > * For searches and help try:
>> > * http://www.stata.com/help.cgi?search
>> > * http://www.stata.com/support/faqs/resources/statalist-faq/
>> > * http://www.ats.ucla.edu/stat/stata/
>>
>> *
>> * For searches and help try:
>> * http://www.stata.com/help.cgi?search
>> * http://www.stata.com/support/faqs/resources/statalist-faq/
>> * http://www.ats.ucla.edu/stat/stata/
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/faqs/resources/statalist-faq/
> *   http://www.ats.ucla.edu/stat/stata/

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/


© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   Site index